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Play with Elm!
Rethink Web Development
About Me
Choucri FAHED
CTO of Finstack
Scala, FP, Elm, Idris, Blockchains, AI, Universal Income… good food
Summary
● Why Elm?
● What’s Elm?
● TEA (The Elm Architecture)
● Elm vs ScalaJS
● Elm in Scala Projects
Why Elm?
Created by Evan Czaplicki in 2012
“If typed functional programming is so great, how come nobody uses it?” Let's be mainstream!
How it feels to learn JavaScript in 2016
Objective: NO RUNTIME ERRORS!
What’s Elm?
● Simple language○ Statically typed, strict, purely functional○ Compiles to JavaScript
● Simple framework / libraries○ TEA (The Elm Architecture)○ Use “Obvious names” No M-word
● Simple and user focused tools○ Friendly compiler error messages○ Time travel debugger, elm-format…○ Automatic semver enforcement with elm-package
Values - Literals
Values - Lists & Tuples
● Lists: All 4 are equivalent below
● Tuples
Since 0.18
Values - Union Types
Values - Records
Functions
What else?
● If and let expressions● No for or while loops● Operators● JavaScript interop with ports● Modules
For more Elm syntax
That’s it?!
● No type classes● No higher kinded types (ex: Functor[F[_]])
○ First order kinds like Monoids supported only
Feel frustrated? Try PureScript
TEA - The Elm Architecture
Simple and amazingly scalable pattern
(overly simplified view below)
Model or Staterecord type(managed)
View(managed by
elm-html)
elm-htmlruntime
view()function
Messagesunion type
update()function
*code you need to write in blue
TEA - Model
TEA - Update
TEA - View
TEA - Main
Since 0.18
Performance
Benchmark: Adding 100 items in the TodoMVC app
Ecosystem
● Write HTML with elm-html● Write CSS with elm-css● Material Design with elm-mdl● Make HTTP calls with elm-http● Unit testing with elm-test● …
Guess the pattern? More Awesome Elm
Learn More
● http://elm-lang.org/● Elm Slack● http://exercism.io/languages/elm● Elm Weekly Newsletter● On Twitter
○ @elmlang○ @czaplic○ @rtfeldman○ @elmcastio○ @elmstuff
Elm vs ScalaJS
ScalaJS Elm
Opinionated No Highly
JS Interoperability Easy Hard (discouraged)
SPA Framework scalajs-react, udash.io elm-html (TEA)
Runtime Size 100KB 10KB
Build Tool SBT elm-package
Semantic Versioning No Yes
IDE Support Excellent in Intellij Excellent in Atom
Debugger Standard IDE tools Time-travel debugger
Ecosystem Huge Small but growing fast
Elm in Scala Projects
SBT Elm plugin
Check out examples folder
Elm records generated from Scala case classes with scala-elm-types
Show time!
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